/*
 * Copyright 2002-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.util;

import java.text.NumberFormat;
import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.TimeUnit;

import org.springframework.lang.Nullable;

/**
 * Simple stop watch, allowing for timing of a number of tasks, exposing total
 * running time and running time for each named task.
 *
 * <p>Conceals use of {@link System#nanoTime()}, improving the readability of
 * application code and reducing the likelihood of calculation errors.
 *
 * <p>Note that this object is not designed to be thread-safe and does not use
 * synchronization.
 *
 * <p>This class is normally used to verify performance during proof-of-concept
 * work and in development, rather than as part of production applications.
 *
 * <p>As of Spring Framework 5.2, running time is tracked and reported in
 * nanoseconds.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Sam Brannen
 * @since May 2, 2001
 */
public class StopWatch {

        /**
         * Identifier of this {@code StopWatch}.
         * <p>Handy when we have output from multiple stop watches and need to
         * distinguish between them in log or console output.
         */
        private final String id;

        private boolean keepTaskList = true;

        private final List<TaskInfo> taskList = new LinkedList<>();

        /** Start time of the current task. */
        private long startTimeNanos;

        /** Name of the current task. */
        @Nullable
        private String currentTaskName;

        @Nullable
        private TaskInfo lastTaskInfo;

        private int taskCount;

        /** Total running time. */
        private long totalTimeNanos;


        /**
         * Construct a new {@code StopWatch}.
         * <p>Does not start any task.
         */
        public StopWatch() {
                this("");
        }

        /**
         * Construct a new {@code StopWatch} with the given ID.
         * <p>The ID is handy when we have output from multiple stop watches and need
         * to distinguish between them.
         * <p>Does not start any task.
         * @param id identifier for this stop watch
         */
        public StopWatch(String id) {
                this.id = id;
        }


        /**
         * Get the ID of this {@code StopWatch}, as specified on construction.
         * @return the ID (empty String by default)
         * @since 4.2.2
         * @see #StopWatch(String)
         */
        public String getId() {
                return this.id;
        }

        /**
         * Configure whether the {@link TaskInfo} array is built over time.
         * <p>Set this to {@code false} when using a {@code StopWatch} for millions
         * of intervals; otherwise, the {@code TaskInfo} structure will consume
         * excessive memory.
         * <p>Default is {@code true}.
         */
        public void setKeepTaskList(boolean keepTaskList) {
                this.keepTaskList = keepTaskList;
        }


        /**
         * Start an unnamed task.
         * <p>The results are undefined if {@link #stop()} or timing methods are
         * called without invoking this method first.
         * @see #start(String)
         * @see #stop()
         */
        public void start() throws IllegalStateException {
                start("");
        }

        /**
         * Start a named task.
         * <p>The results are undefined if {@link #stop()} or timing methods are
         * called without invoking this method first.
         * @param taskName the name of the task to start
         * @see #start()
         * @see #stop()
         */
        public void start(String taskName) throws IllegalStateException {
                if (this.currentTaskName != null) {
                        throw new IllegalStateException("Can't start StopWatch: it's already running");
                }
                this.currentTaskName = taskName;
                this.startTimeNanos = System.nanoTime();
        }

        /**
         * Stop the current task.
         * <p>The results are undefined if timing methods are called without invoking
         * at least one pair of {@code start()} / {@code stop()} methods.
         * @see #start()
         * @see #start(String)
         */
        public void stop() throws IllegalStateException {
                if (this.currentTaskName == null) {
                        throw new IllegalStateException("Can't stop StopWatch: it's not running");
                }
                long lastTime = System.nanoTime() - this.startTimeNanos;
                this.totalTimeNanos += lastTime;
                this.lastTaskInfo = new TaskInfo(this.currentTaskName, lastTime);
                if (this.keepTaskList) {
                        this.taskList.add(this.lastTaskInfo);
                }
                ++this.taskCount;
                this.currentTaskName = null;
        }

        /**
         * Determine whether this {@code StopWatch} is currently running.
         * @see #currentTaskName()
         */
        public boolean isRunning() {
                return (this.currentTaskName != null);
        }

        /**
         * Get the name of the currently running task, if any.
         * @since 4.2.2
         * @see #isRunning()
         */
        @Nullable
        public String currentTaskName() {
                return this.currentTaskName;
        }

        /**
         * Get the time taken by the last task in nanoseconds.
         * @since 5.2
         * @see #getLastTaskTimeMillis()
         */
        public long getLastTaskTimeNanos() throws IllegalStateException {
                if (this.lastTaskInfo == null) {
                        throw new IllegalStateException("No tasks run: can't get last task interval");
                }
                return this.lastTaskInfo.getTimeNanos();
        }

        /**
         * Get the time taken by the last task in milliseconds.
         * @see #getLastTaskTimeNanos()
         */
        public long getLastTaskTimeMillis() throws IllegalStateException {
                if (this.lastTaskInfo == null) {
                        throw new IllegalStateException("No tasks run: can't get last task interval");
                }
                return this.lastTaskInfo.getTimeMillis();
        }

        /**
         * Get the name of the last task.
         */
        public String getLastTaskName() throws IllegalStateException {
                if (this.lastTaskInfo == null) {
                        throw new IllegalStateException("No tasks run: can't get last task name");
                }
                return this.lastTaskInfo.getTaskName();
        }

        /**
         * Get the last task as a {@link TaskInfo} object.
         */
        public TaskInfo getLastTaskInfo() throws IllegalStateException {
                if (this.lastTaskInfo == null) {
                        throw new IllegalStateException("No tasks run: can't get last task info");
                }
                return this.lastTaskInfo;
        }


        /**
         * Get the total time in nanoseconds for all tasks.
         * @since 5.2
         * @see #getTotalTimeMillis()
         * @see #getTotalTimeSeconds()
         */
        public long getTotalTimeNanos() {
                return this.totalTimeNanos;
        }

        /**
         * Get the total time in milliseconds for all tasks.
         * @see #getTotalTimeNanos()
         * @see #getTotalTimeSeconds()
         */
        public long getTotalTimeMillis() {
                return nanosToMillis(this.totalTimeNanos);
        }

        /**
         * Get the total time in seconds for all tasks.
         * @see #getTotalTimeNanos()
         * @see #getTotalTimeMillis()
         */
        public double getTotalTimeSeconds() {
                return nanosToSeconds(this.totalTimeNanos);
        }

        /**
         * Get the number of tasks timed.
         */
        public int getTaskCount() {
                return this.taskCount;
        }

        /**
         * Get an array of the data for tasks performed.
         */
        public TaskInfo[] getTaskInfo() {
                if (!this.keepTaskList) {
                        throw new UnsupportedOperationException("Task info is not being kept!");
                }
                return this.taskList.toArray(new TaskInfo[0]);
        }


        /**
         * Get a short description of the total running time.
         */
        public String shortSummary() {
                return "StopWatch '" + getId() + "': running time = " + getTotalTimeNanos() + " ns";
        }

        /**
         * Generate a string with a table describing all tasks performed.
         * <p>For custom reporting, call {@link #getTaskInfo()} and use the task info
         * directly.
         */
        public String prettyPrint() {
                StringBuilder sb = new StringBuilder(shortSummary());
                sb.append('\n');
                if (!this.keepTaskList) {
                        sb.append("No task info kept");
                }
                else {
                        sb.append("---------------------------------------------\n");
                        sb.append("ns         %     Task name\n");
                        sb.append("---------------------------------------------\n");
                        NumberFormat nf = NumberFormat.getNumberInstance();
                        nf.setMinimumIntegerDigits(9);
                        nf.setGroupingUsed(false);
                        NumberFormat pf = NumberFormat.getPercentInstance();
                        pf.setMinimumIntegerDigits(3);
                        pf.setGroupingUsed(false);
                        for (TaskInfo task : getTaskInfo()) {
                                sb.append(nf.format(task.getTimeNanos())).append("  ");
                                sb.append(pf.format((double) task.getTimeNanos() / getTotalTimeNanos())).append("  ");
                                sb.append(task.getTaskName()).append("\n");
                        }
                }
                return sb.toString();
        }

        /**
         * Generate an informative string describing all tasks performed
         * <p>For custom reporting, call {@link #getTaskInfo()} and use the task info
         * directly.
         */
        @Override
        public String toString() {
                StringBuilder sb = new StringBuilder(shortSummary());
                if (this.keepTaskList) {
                        for (TaskInfo task : getTaskInfo()) {
                                sb.append("; [").append(task.getTaskName()).append("] took ").append(task.getTimeNanos()).append(" ns");
                                long percent = Math.round(100.0 * task.getTimeNanos() / getTotalTimeNanos());
                                sb.append(" = ").append(percent).append("%");
                        }
                }
                else {
                        sb.append("; no task info kept");
                }
                return sb.toString();
        }


        private static long nanosToMillis(long duration) {
                return TimeUnit.NANOSECONDS.toMillis(duration);
        }

        private static double nanosToSeconds(long duration) {
                return duration / 1_000_000_000.0;
        }


        /**
         * Nested class to hold data about one task executed within the {@code StopWatch}.
         */
        public static final class TaskInfo {

                private final String taskName;

                private final long timeNanos;

                TaskInfo(String taskName, long timeNanos) {
                        this.taskName = taskName;
                        this.timeNanos = timeNanos;
                }

                /**
                 * Get the name of this task.
                 */
                public String getTaskName() {
                        return this.taskName;
                }

                /**
                 * Get the time in nanoseconds this task took.
                 * @since 5.2
                 * @see #getTimeMillis()
                 * @see #getTimeSeconds()
                 */
                public long getTimeNanos() {
                        return this.timeNanos;
                }

                /**
                 * Get the time in milliseconds this task took.
                 * @see #getTimeNanos()
                 * @see #getTimeSeconds()
                 */
                public long getTimeMillis() {
                        return nanosToMillis(this.timeNanos);
                }

                /**
                 * Get the time in seconds this task took.
                 * @see #getTimeMillis()
                 * @see #getTimeNanos()
                 */
                public double getTimeSeconds() {
                        return nanosToSeconds(this.timeNanos);
                }

        }

}